Similar Projects

Overview

Medium-density fiberboard is the
most versatile building material
I know of. Because it’s inexpensive and
fairly durable, it’s a good choice for
practical projects like shelving and storage
cabinets. But MDF is great for decorative
projects too. The smooth surface
is perfect for painting, and a router
leaves crisp profiles with no splintering,
burning or tear-out.

Over the past 15 years, I’ve used
MDF to build everything from crude
shelving in my shop to fancy trim in
upscale homes. I’ve even used it for
furniture and ornate millwork like the
trim board shown in the lead photo. In fact, my
own home is entirely trimmed out with
MDF moldings made from about 50
sheets of MDF. Yes, I’m a fan of the
stuff. This article will cover the most
important things I’ve learned about
working with MDF—and help you
avoid some of the frustrating mistakes
I’ve made.

MDF is basically sawdust and glue,
fused together under pressure and heat.
It varies in color from tan to chocolate
brown. Common thicknesses range
from 1/4 in. to 1 in., but most home
centers carry only 1/2-in. and 3/4-in.
Full sheets are oversized by 1 in., so a
“4 x 8” sheet is actually 49 x 97 in. A
full sheet of 3/4-in. MDF costs about
$30 (as of 2010). Some home centers also carry
MDF boards in various lengths and
widths. Working with MDF is no different
from working with wood or plywood;
you use the same tools to cut and
shape it.

Make your own trim—cheap!

Cut any profile

When a job calls for painted trim, I almost
always cut costs with MDF. Even inexpensive
wood, like this poplar baseboard, costs four
times as much. To make trim, I cut MDF
sheets into strips and shape the edges with a
router or router table. With the right bit, I can
create just about any trim profile, simple or
fancy. (Check woodworking stores or online for a large selection of bits.) Some home centers carry ready-made
MDF trim for less than the price of solid wood.

Combine MDF with wood moldings

Mix and match

Here’s one of my favorite tricks for painted trim, cabinets or even furniture:
Use MDF for the large, plain parts and dress them up with wood moldings like
base cap, coves or base shoe. That gives you the money savings of MDF without
the time-consuming work of making MDF trim from scratch. The wainscoting
shown here, for example, is simply panels and strips of 1/2-in. MDF
trimmed with inexpensive, small-profile pine moldings. The
cap rail is likely to take a beating from chairs, so I make that from wood instead
of MDF. Once coated with primer and paint, the wood and MDF parts will look
exactly the same.

Prepare for a dust storm

Wear a good mask

There’s one thing you’ll really hate about MDF: the fine, powdery dust that
invades your clothes, hangs in the air for hours and clings to every surface like
a coat of frost. Cutting MDF is a dusty job, but routing it is even worse.

Whenever possible, I cut and rout MDF outside. When that’s not possible, I
drape sheets of plastic over shelving and other hard-to-clean areas in my shop
and use a fan to blow dust outside. When installing trim in a room, cover doorways,
close air vents and expect to vacuum every surface when you’re done,
even the walls. Clean your vacuum filter often—the fine dust plugs filters quickly. And a tight-fitting dust mask is essential.

Don't drive without drilling

Avoid splits and cracks

MDF is kind of like an Oreo cookie: two
hard faces with a softer core between
them. That soft core splits easily when
you drive a screw into the edge. The
hard face presents different problems
for screws. If you don’t drill a countersink
recess, the screw head may snap
off before it sinks into the MDF. Or, if
the head does sink, it might push up
chips. The cure for both problems is to
use a countersinking drill bit.

Countersink bit

A countersink bit gives you a pilot hole
and a recess for the
screw head in
one step. They're available at any hardware store or home center.

Sand, prime, sand...

Use solvent-based primer

The face of MDF is smooth, but the
edges are fuzzy like the skin of a
peach. If you just slap paint on the
fuzz, it will look and feel like sandpaper.
So you have to get rid of the
peach fuzz before you paint. I have
two recipes for smooth edges: one for
“good-enough” edges and the other for
edges that will get a high-gloss finish.

Here’s the good-enough process I
apply to most projects, including
trim: First, lightly sand the edges with
100-grit paper. Foam-backed sanding
pads work great on routed profiles.
Then prime the MDF. Use a solvent-based
primer only. Water-based
primer can raise small blisters. My
favorite MDF primers are KILZ and
Cover Stain because they’re easy to
sand. When the primer dries, sand off
the fuzz with 100-grit pads. A couple
of light passes is all it takes. You can
sand KILZ or Cover Stain after a couple
of hours, but let the primer dry overnight for smoother results. After
sanding, wipe away the powdery dust
with a damp cloth and you’re ready to
paint.

Prime and sand high-gloss edges twice

For projects that will get a coat of
high-gloss paint, I prime twice: First I
prime the edges only. Later I prime
the whole project (as described
above). When applying the edge-only
coat, be sure to feather out any primer
on the face of the MDF so brush marks
won’t show up later. Then sand,
prime again and sand again to achieve
smooth-as-glass edges.

Don't drop it

Avoid rough handling

The face of MDF is harder than most
woods, but the inner layers are soft. So
edges, and especially corners, are easy
to crush. That means you have to handle
it with more care than lumber or
plywood. Also, avoid scratching the
face. Light scratches stand out like a
sore thumb on the ultra-smooth surface,
so you have to sand them out
completely before priming. And wear
gloves when handling MDF, especially
when carrying heavy sheets. MDF
edges can be sharp enough to cut skin—I’ve got the scars to prove it.

Don't let it get wet

Water kills MDF

MDF stands up to moisture about as well as graham crackers. A few water
drops will raise small bumps on the surface. A long soaking will make it swell
to twice its original thickness. So MDF is a risky choice for baseboards in entryways
and trim near tubs or sinks. My all-time greatest MDF mistake was using
it for windowsills in my own home. Condensation from the windows made
them swell just like the baseboard shown here. If you use MDF as baseboard,
be sure to paint the lower edge before installation. That will provide short-term
protection against occasional spills. Also install the baseboard about 1/4 in.
above the floor and then cover the gap with wood base shoe molding. There are
moisture-resistant versions of MDF, but they’re hard to find. To find manufacturers and dealers, search online for “moisture resistant MDF.”

Reinforce MDF shelves

Guard against sagging

MDF is commonly used for shelving
in closets and cabinets because it’s
inexpensive and smooth. But MDF
isn’t as stiff as plywood and will sag
over time. So when I use MDF shelving
for heavy loads, I simply beef it
up with wood. First, I rip a 1x4 right
down the middle to get two strips
about 1-5/8 in. wide. I glue one strip
flat against the underside of the shelf
to stiffen the back edge. Then I glue
the other strip (nosing) to the front
edge. The MDF edge will absorb a lot
of glue, so spread on a light coat, give
it a minute to soak in, and apply
another bead before you add the
wood nosing.

Don't use a hammer

Power nailers work best

Unless you’re willing to drill a hole
for every single nail, don’t plan on
using a hammer. Without a hole, the
nail will probably bend in rock-hard
MDF. And even if it goes in without
bending, the nail will push up a
mound of fiber that looks like a mini
volcano. A trim nailer, on the other
hand, shoots nails through MDF
every time. The skinny nails will
raise tiny pimples, but you can easily
scrape them off with a sharp putty
knife before you fill the nail holes.